1. Field of the Invention
This invention relates to the field of the measurement of the characteristics of thin films and, more particularly, to the measurement of the thickness and refractive index of thin films by means of optical techniques.
2. Description of the Prior Art
In order to measure the thickness and refractive index of a thin film on a substrate, various optical techniques have been employed in the prior art. Ordinarily these techniques involve measurements of the intensity and polarization of the transmitted or reflected light from the thin film, as a function of angular orientation ("ellipsometry"). However, the use of these techniques generally tends to be unduly time-consuming. While the more rapid techniques using rotating analyzer ellipsometry have been used in the prior art, such techniques suffer from ambiguities and do not yield correct results in the presence of diffuse reflectance.
In U.S. Pat. No. 3,873,209 issued to Schinke et al. on Mar. 25, 1975, an optical thin film waveguide technique was described for measuring the thickness and refractive index of a thin film. In that technique, an evanescent optical wave is coupled into the film; and the resulting optical intensity minima, characterizing the light which is coupled out of the film as a function of angle, yield data from which the desired thin film thickness and refractive index can be determined. It would be desirable, however, to have a relatively fast thickness measurement technique which does not require the operator to locate such minima.